Easily, you can view all of root safely within your file manager. If using Nautilus (The default
Files) then click the "other locations" selection in the Left Sidepane.
Then Computer - and start at Root. You can see
var listed as a directory. You will not have
write permissions to change anything unless you elevate to root. But I wouldn't recommend doing that until you have used the OS a little while and grown familiarity.
Without access to your drive, we cannot tell you what is taking up space.
Open a terminal with the keyboard shortcut ctrl+alt+t and run the command:
sudo apt install ncdu
Once it is installed, run
This will print out your Space Hogs on the drive. (There is also a good packages for doing this included in the Debian Goodies bundle, but I am in a hurry and cannot go searching that right now. I posted a thread about it back in prehistory...)